* improve extractCandidates
When we have a css rule that is defined as `.foo, .bar {}`, then we will
crawl each selector and link it to the same node. This is useful because
now our Map looks something like this:
```js
Map(2) { 'foo' => Node {}, 'bar' => Node {} }
```
This allows us to later on `@apply foo` or `@apply bar` and we can do a
direct lookup for this "candidate".
When we have css defined as `span {}`, then we consider this
"non-ondemandable". This means that we will _always_ inject these rules
into the `*` section and call it a day.
However, it could happen that you have something like this: `span, .foo
{}` up until now this was totally fine. It contains a non-ondemandable
selector (`span`) and therefore we injected this into that `*` section.
However, the issue occurs if you now try to `@apply foo`. Since we had
an early return for this use case it didn't endup in our Map from above
and now you get an error like:
```
The `foo` class does not exist. If `foo` is a custom class, make sure it
is defined within a `@layer` directive."
```
So instead what we will do is keep track whether or not a css rule
contains any on-demandable classes. If this is the case then we still
generate it always by putting it in that `*` section. However, we will
still register all on-demandable classes in our Map (in this case `.foo`).
This allows us to `@apply foo` again!
* update changelog
21fe083db0